Re: But... why?
For example in IPV4, if someone did 12.34.56.78/8, some programs would just assume that to mean 12.0.0.0/8.
Yup, that's correct, ie IPv4 and v6 work on an address, and the netmask/route. Programmes shouldn't rewrite or assume it means 12.0.0.0, but should route as being part of 12/8
IPv6 complicates things with a lot more reserved addresses & scopes.. But xxx.0 has always been a bit special, hence the comment about subnet zero, which was to counter a hold-over from pre-CIDR days and the first address being the broadcast address. Which becomes irrelevant on a P2P link with only 2 endpoints. Many v4 addresses have been wasted by people using /30's instead of /31. So it could have been an attempt at configuring a link, or misconfiguring anycast.
Either way, the /127 route shouldn't have escaped into the global table when that ideally wouldn't contain anything more specific than /56 customer allocations.. Which is back to Cloudflare scenarios and ISPs not having sensible route filters.
Biting the hand that feeds IT
